“Markers” or “taggants” are terms used to represent any material that can be added to explosives, chemical weapons, etc. in order to assist in identifying the explosive/weapon or its source before, after, or both before and after its detonation or use. While the motive for including such markers or taggants in explosives and other weapons is clearly anti-terrorism, taggants have also been proposed as anti-counterfeiting devices, anti-tampering devices, and as quality control devices in commercial products ranging from gasoline to perfumes (“Black and Smokeless Powders: Technologies for Finding Bombs and the Bomb Makers,” Committee on Smokeless and Black Powder, National Research Council, 1998).
While such markers or taggants can aid authorities in their investigation of detonated explosives or deployed chemical weapons and in identifying the source of such seized weapons, they generally cannot prevent the harmful agent from being used. Furthermore, the taggants must be inserted during the production of the harmful agent. This means that weapons or other harmful devices fabricated by terrorist elements or rogue nations would likely be unidentifiable.
One way of overcoming the above-mentioned limitations is to devise strategies for chemically sensing explosives, chemical weapons, and other harmful agents by exploiting the high vapor pressures that many of them possess and the emission of nitrogen- and phosphorus-containing free radicals from the explosives, chemical weapons, and other harmful agents. This is the case for phosphorus-containing chemical nerve agents like sarin, soman, tabun, and VX and for nitro-containing explosives like trinitrotoluene (TNT) and nitroglycerine. Chemical sensing, such as utilizing spectral characteristics, could be used to detect such harmful materials in public places like airports, subways, shopping malls, etc. This would allow for the pre-emptive identification of harmful materials, before they have inflicted any damage.